Treatment of coal

ABSTRACT

Process for treating coal by feeding a first batch of raw coal to a first dryer to remove moisture contained in the raw coal to produce demoisturized coal; feeding the demoisturized coal to a devolatilizer to remove volatile material from the demoisturized coal to produce devolatilized coal; feeding a first portion of the devolatilized coal to a combustor to provide heat for the process; feeding a second portion of the devolatilized coal to a coater; feeding a second batch of raw coal to a slave dryer to produce a second batch of demoisturized coal; feeding the second batch of demoisturized coal to the coater where the second portion of devolatilized coal and the second batch of demoisturized coal are coated with volatile material produced in the devolatilizer, to produce a stabilized coal product; and collecting the stabilized coal product.

TECHNICAL FIELD

The present invention relates to the treatment of coal. More particularly, the present invention provides a process for treating coal by removing moisture only and to produce a stable fuel product, increasing the heating value of the fuel product, and stabilizing the product to prevent re-absorption of moisture, degradation, and spontaneous combustion.

BACKGROUND OF THE INVENTION

Prior processes for treating coal remove moisture and unwanted volatile matter from the coal (typically low-rank coals and lignite) to produce coal of higher quality, with increased heat release per unit mass of fuel. For example, U.S. Pat. Nos. 6,447,559 and 7,879,117 describe processes for producing a clean coal fuel that has a higher heating value per unit mass of coal compared to the raw coal. The clean coal fuel also produces zero or minimal emissions. The volatile matter removed from the raw coal is used as a fuel to provide process heat.

The prior processes remove both moisture and volatile matter in several (2-4) different stages. Typically, the first stage removes only moisture from the coal, while the remaining stages remove volatile matter as light and heavy hydrocarbons. However, the removal of only moisture from coal is not as simple as removing, from the prior process, the latter stages that remove volatile matter. Moreover, removal of moisture only from low-rank coal and lignite is known to produce an unstable coal fuel that can spontaneously ignite, disintegrate into a powder, and re-absorb moisture. These undesirable properties limit the shelf life of the de-moisturized coal.

To date, no one has successfully developed a process that can remove moisture only from low-rank coal and lignite and produce a stable product. Furthermore, because no volatiles are removed from the coal, there is no internally produced fuel to meet the heat demands of the process. Consequently, an external source of heat is required if the prior processes are to be modified to only remove moisture from low rank coals and lignite. The provision of heat from an external source adds to the capital and operating costs of such processes

SUMMARY OF THE INVENTION

It has now been discovered, according to the present invention, that it is possible to treat coal is such a way as to remove only the moisture and yet produce a stable product with increased heating values per unit mass compared with the feed coal. According to a first aspect, there is provided a process for treating coal comprising the steps of:

feeding a first batch of raw coal to a first dryer to remove moisture contained in the raw coal to produce a first demoisturized coal;

feeding the first demoisturized coal to a devolatilizer to remove volatile material from the first demoisturized coal to produce a devolatilized coal;

feeding a first portion of the devolatilized coal to a combustor to provide heat for the process;

feeding a second batch of raw coal to a slave dryer to produce a second demoisturized coal;

feeding the second demoisturized coal to the coater where the second portion of the devolatilized coal and the second demoisturized coal are coated with volatile material produced in the devolatilizer, to produce a stabilized coal product; and

cooling and collecting the stabilized coal product.

In a further aspect there is provided treated coal produced according to the process of the invention.

In another aspect, the invention provides briquettes formed from coal treated according to the process of the invention. The briquettes may be provided with a waterproof coating to improve stability, ignition properties and to extend shelf life.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the invention will now be described in more detail with reference to the accompanying Figure which is a flow diagram of the process of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the Figure, there is shown a flow diagram of the present invention. In the Figure, the flow rates shown correspond to a plant processing 180 tons per hour (tph) of raw coal, of which a portion, 30 tph (i.e., “the first batch”), is used for providing heat for the process. It will be understood that the process of the invention is not limited to those particular feed rates.

The apparatus employed in the process of the invention includes a master dryer 2, a devolatilizer 4, a combuster 6, a series of slave dryers 8, 10, 12, 14 and 16 and a series of coaters 18, 20, 22, 24 and 26. A first batch of raw coal (30 tph) is fed to the master dryer 2 to remove moisture contained in the raw coal. The term “remove moisture”, as used herein, means that the content of moisture (water) in the coal is reduced to less than 5% by weight, for example 2-4% by weight.

The resulting demoisturized product is then fed to the devolatilizer 4 to remove volatile material in the coal. The term “remove volatile material”, as used herein, means that the content of volatile material in the coal is reduced to less than 5% by weight, for example 2-4% by weight. These two steps of moisture removal and volatile material removal are accomplished as in U.S. Pat. No. 6,447,559 (herein incorporated by reference) in one unit operation.

The coal exiting the devolatilizer (17.6 tph) is split into two streams. The first stream (6.1 tph) is fed to combustor 6 where heat generated is fed to the master dryer 2, the devolatilizer 4 and the slave dryers 8, 10, 12, 14, and 16.

A second batch of raw coal is fed directly to the respective slave dryers 8, 10, 12, 14, 16 where the coal dried to a moisture level of about 5 wt %. The slave dryers 8-16 are heated with heat from the combustor 6 to remove only moisture from the incoming second batch of coal.

As simple moisture removal produces an unstable coal product, the demoisturized coal from each of the slave dryers is passed through respective coaters 18, 20, 22, 24, 26, where it is mixed with the remainder (11.5 tph) of the first batch of raw coal that has been demoisturized and devolatilized in the master dryer 2 and devolatilizer 4, respectively. The coaters may be heated using heat from the combustor 6, if needed. Volatile material produced by the devolatilizer 4 is fed to the respective coaters to coat the coal and thereby produce a stabilized coal, which is then collected from the coaters.

An important feature of the invention is coating of the demoisturized coal produced by the respective slave dryers in a separate operation using volatile material withdrawn from the coal in the devolatilizer 4. The application of the volatile material onto the demoisturized coal in the coaters may be effected, for example, by immersion of the demoisturized coal in volatile material condensate or by allowing vapors from the volatile material to condense on the surface of the demoisturized coal.

The volatile material condensate from the devolatilizer 4 contains tars, anthracene oils, and other coal derivatives. Coating the demoisturized coal in the coaters with this volatile material condensate is believed to seal the pore structure of the coal and prevent it from reabsorbing moisture, disintegrating into a powder, and/or undergoing spontaneous self-ignition and combustion.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, and is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. 

What is claimed is:
 1. A process for treating coal comprising the steps of: feeding a first batch of raw coal to a first dryer to remove moisture contained in the raw coal to produce a first demoisturized coal; feeding the first demoisturized coal to a devolatilizer to remove volatile material from the first demoisturized coal to produce a devolatilized coal; feeding a first portion of the devolatilized coal to a combustor to provide heat for the process; feeding a second portion of the devolatilized coal to a coater; feeding a second batch of raw coal to a slave dryer to produce a second demoisturized coal; feeding the second demoisturized coal to said coater where the second portion of the devolatilized coal and the second demoisturized coal are coated with volatile material produced in the devolatilizer, to produce a stabilized coal product; and collecting the stabilized coal product.
 2. The process according to claim 1 wherein the volatile material is applied to the second portion of the devolatilized coal and the second demoisturized coal by immersion in condensed volatile material.
 3. The process according to claim 1 wherein the volatile material is applied to the second portion of the devolatilized coal and the second demoisturized coal by condensing vapor of volatile material on the surface of the coal.
 4. Treated coal produced according to the process of claim
 1. 5. Treated coal according to claim 4, provided with a waterproof binder/igniter/coating.
 6. Treated coal according to claim 4 in the form of briquettes.
 7. Briquettes according to claim 6 provided with a water-proof binder/igniter/coating. 